E.,
You are very young. You have much time. You already have a child. It would seem your obstacles are few. I recommend you start evaluating your body more naturally and determine where the imbalance is. Any symptom is simply a signal to you of imbalance. View it as an opportunity to LEARN something about yourself and where you are in your life. Listen to it and try to bring it back into balance. For example, how does getting pregnant again make you FEEL. It must be somewhat daunting to think about doing it all over again now that your first child is 8. It must have been hard to have a child at 16, and go through all the very tough stages of early childhood. How does all of that history make you FEEL about getting pregnant now. It has nothing to do with your love for your current partner and conscous desire for more family. Of course you want this. But is there maybe a little teeny weeny part of you that thinks "gee, maybe I'm not ready to do all that again"? These may not be your feelings, but they are an example of the type of emotional ambivalence that can impact fertility.
Did you see the response from the mom who had a low thyroid that nobody checked? This is common. They are quick with the drugs, and slow on the uptake when it comes to improved health. Improved health, both mental and physical well being, is your ticket to a successful pregnancy and child.
Recommended reading for you:
Women's Bodies, Women's Wisdom by Dr. Christiane Northrup
The Whole Person Fertility Program by Niravi Payne
The Fertility Cure by Randine Lewis
Wise Woman for the Childbearing Year by Susun Weed
For practitioner's in the area to help you understand your preconception health better and all the many factors that can and will impact your fertility (e.g. ovulation cycle, hormone levels, anxieties and worries, nutrition, sleep issues, relationship issues, etc.) you might try Dr. Margaret Christensen. She is at the corner of White Rock Lake Trail and Walnut Hill. She will get you on the right track to understanding your body. Ask to be put on the waiting list. If they can't see you, which I doubt, ask for another referral to someone likeminded.
By the way, if you properly understand your body signals, you should be able to tell when you are ovulating without the help of strips, test kits, sonos, or psychic consultations. If you don't, you have some work to do in understanding your very own miraculous body that you walk around in every day. Oh, and don't ask your ob/gyn for help with this. They don't understand it either. Start with Dr. Northrup's book, available at most Half Price Books and Sam's; she will help you with that. Highly recommend this book and all others by Dr. Northrup!!
Joy to you and your family!
Good luck!!